Calendar age and total days describe the same interval using different units. To compare them, keep the reference date fixed and read the labels alongside the figures.
For a birth on March 1, 2023 and a reference date of March 1, 2024, the calculator shows one completed year and 366 total days. February 29 lies inside that interval. Dividing 366 by 365 would describe an approximate duration in fixed-length years rather than completed birthdays.
What happens at month end
Enter January 31, 2000 and February 29, 2024. Under the tool's month-end rule, the result is 24 years and one month. January 31 plus one calendar month is clamped to February 29 because February has no 31st.
The tool anchors months after the most recent completed birthday. It does not repeatedly add one month from each previous truncated date. Repeatedly moving a January 31 date to February 28 and then to March 28 would lose the original monthly anchor.
Which output to copy
Use Years, Months, and Days for a calendar-age caption. Use Total Days Lived when comparing a day milestone. Total Weeks counts complete seven-day blocks and omits the remaining days.
If you count the day of birth as Day 1, add one to elapsed days for that separate convention and label it accordingly. The calculator's total is the elapsed interval.